• Research Article
• Open Access

# Sharpening the Becker-Stark Inequalities

Journal of Inequalities and Applications20102010:931275

https://doi.org/10.1155/2010/931275

• Received: 3 April 2009
• Accepted: 14 January 2010
• Published:

## Abstract

In this paper, we establish a general refinement of the Becker-Stark inequalities by using the power series expansion of the tangent function via Bernoulli numbers and the property of a function involving Riemann's zeta one.

## Keywords

• Power Series
• Natural Number
• Series Expansion
• Zeta Function
• Power Series Expansion

## 1. Introduction

Steckin  (or see Mitrinovic [2, 3.4.19, page 246]) gives us a result as follows.

Theorem 1.1 (see [1, Lemma ]).

If , then

Later, Becker and Stark  (or see Kuang [4, 5.1.102, page 248]) obtain the following two-sided rational approximation for .

Theorem 1.2.

Let , then

Furthermore, and are the best constants in (1.2).

In fact, we can obtain the following further results.

Theorem 1.3.

Let , then

Furthermore, and are the best constants in (1.3).

In this paper, in the form of (1.2) and (1.3) we shall show a general refinement of the Becker-Stark inequalities as follows.

Theorem 1.4.

Let , and let be a natural number. Then
holds, where , and

where are the even-indexed Bernoulli numbers.

Furthermore, and are the best constants in (1.4).

## 2. Four Lemmas

Lemma 2.1.

The function is decreasing, where is Riemann's zeta function.

Proof.

is equivalent to the function , which is decreasing.

Lemma 2.2 (see [5, Theorem ]).

Let be Riemann's zeta function and the even-indexed Bernoulli numbers. Then

Lemma 2.3 (see [6, 1.3.1.4 (1.3)]).

Let . Then

Lemma 2.4.

Let and . Then , where

Proof.

Since is decreasing by Lemma 2.1, it follows that

which implies that for .

## 3. Proofs of Theorems

Proof of Theorem 1.4.

By Lemma 2.4, we have for , and is decreasing on .

At the same time, = by (3.1), and by (3.2), so and are the best constants in (1.4).

Proof of Theorem 1.3.

Let in Theorem 1.4; we obtain that and . Then the proof of Theorem 1.3 is complete.

## Authors’ Affiliations

(1)
Department of Mathematics, Zhejiang Gongshang University, Hangzhou, Zhejiang, 310018, China

## References 